Filament or fibre

ABSTRACT

A filament or fibre ( 2 ) comprising: a first conductive layer ( 4 ); an electro-optically active layer ( 6 ); a second conductive layer ( 8 ); wherein the filament or fibre has an off-state and an on-state, the electro-optically active layer comprising a combination of an electro-optically active substance and a polymer.

This invention relates a fibre or filament, especially one that issuitable for inclusion in a fabric or garment with the aim of producingoptically detectable effects therein.

Various methods of producing colour changing, or light emitting fibresare known.

One known method is based on the use of an electrolumiphore materialwhich emits light under the influence of an electric field. Such amethod is described in UK patent application No. GB 2273606 andInternational patent application No. WO 97/15939. The electric fieldused in such methods is created by integrating at least two electrodesin a fibre.

Other known methods also make use of specific thermochromic materials,i.e., materials that change colour under the influence of a change intemperature. Such a method is disclosed in European patent publicationNo. EP 0410415.

Other known methods have used liquid crystalline material aselectro-optically active material for forming a filament or fibreadapted to have optically detectable effects.

A problem associated with liquid crystal based active layers is theinherit lack of sufficient mechanical stability associated with liquidcrystalline materials. As the liquid crystal layer constitutes primarilylow molecular weight components, the overall material behaviour is thatof a liquid or liquid-like layer. This greatly complicates theconstruction and processing of a fibre or filament. When it is requiredto apply an overlying second electrode, the process is extremelycumbersome and problematic.

In addition, the achievable contrast of pure liquid crystal based layersis often insufficient, and additional functional layers are required,such as polarizers or brightness enhancement layers.

It is an object of the present invention to provide a filament or fibrehaving at least one optical property that is controllably alterable, andin which the filament or fibre has improved mechanical stability.

According to a first aspect of the present invention there is provided afilament or fibre comprising:

-   -   a first conductive layer;    -   an electro-optically active layer;    -   a second conductive layer;    -   wherein the filament or fibre has an off-state and an on-state,        the electro-optically active layer comprising a combination of        an electro-optically active substance and a polymer.

The electro-optically active layer may comprise flexible polymers,side-chain liquid crystal polymers, main-chain liquid crystallinepolymers, isotropic or anisotropic network type structures, of covalentor non-covalent, supramolecular nature, or dispersed polymer particles.

The presence of a polymer in the electro-optically active layer canproduce a stabilising effect on the mechanical properties of thefilament or fibre which increases the manufacturing options andsimplifies processing.

Advantageously, the electro-optically active substance comprises aliquid crystalline material.

Liquid crystalline materials of the type generally used forelectro-optical applications have a low molecular weight. By combiningsuch a material with a high molecular weight polymer, the properties ofthe electro-optically active layer will become less liquid-like and moresolid-like.

The properties of the electro-optically active layer may be tailored toproduce a filament or fibre with appropriate properties, by usingappropriate proportions of polymer and liquid crystalline material.

In other words, the polymer forming part of the electro-optically activelayer will change the mechanical material behaviour of the liquidcrystalline material from liquid-like (for pure low molecular weightliquid crystal materials) to more solid-like. This results in moremechanically stable behaviour, thus making the use of liquid crystalbased effects more realistic for, for use in, for example, textileelectronics.

A further advantage of using a combination of an electro-opticallyactive substance and a polymer to form the electro-optically activelayer in the filament or fibre is that reduced driving voltages,improved contrast, enhanced viewing angles (reduced off-axes haze) (seefor instance Yang, D.-K., Chien, L.-C., Doane, J. W., Appl. Phys. Lett.,60, p. 3102, 1992), are achievable when compared with filaments orfibres in which the electro-optically active layer comprises solelyliquid crystalline material.

These improvements are known from the electro-optical characterizationof conventional liquid crystal display applications. Switching voltagesof twisted nematic (TN) devices of the order of 2-3 V can for instancebe lowered to approximately 1 V when stabilized with 2% polymer. See forinstance Bos, P. J., Rahman, J., Doane, J. W., SID Dig. Tech. Pap., 24,p. 877, 1993. Similar findings are observed for super twisted nematic(STN) devices.

In addition, it is possible to reduce or eliminate defects such asstripe deformations in 270° super twisted nematic liquid crystals. Seefor instance Bos, P. J., Fredley, D., Li, J., Rahman, J. in “Liquidcrystals in complex geometries. Formed by polymer and porous networks”,Crawford, G. P., Zumer, S. (Eds.), Chapter 13, Taylor & Francis, London,1996.

The liquid crystalline material may comprise any suitable liquid crystalor mixture of liquid crystals such as liquid crystals used for TN or STNconfigurations.

The combination of an electro-optically active substance, such as aliquid crystalline substance, and a polymer to form theelectro-optically active layer in the filament or fibre, can consist ofa homogeneous or inhomogeneous mixture, depending on the ratio of theconstituents and the manufacturing conditions, of which thepolymerisation conditions can be an important aspect.

Advantageously, the electro-optically active layer comprises a polymercontent of between 0.5 to 40%.

Preferably, the electro-optically active layer comprises a polymerstabilized ferro-electric or anti-ferro-electric liquid crystallinematerial. Such a layer may be used to create extremely fast switchingfilaments or fibres with typical switching rates in the range from 200ms to 20 ms.

In another preferred embodiment of the present invention theelectro-optically active material comprises a polymer stabilized chiral,nematic or cholesteric fibre. Fibres incorporating such anelectro-optically active layer may also include colours that can beaccurately tuned. Chiral nematic or cholesteric liquid crystals show apolarization-selective reflection provided the wavelength of thecircularly polarized incoming light fulfils the reflection condition:λ= n·p

where λ is the wavelength of the reflected light, n is the averagerefractive index of the liquid crystal, and p is the pitch length of thehelix of the liquid crystal director. One handedness of the incomingcircularly polarized light is absorbed and reflected, whereas the otherhandedness is transmitted, provided a monolithically aligned liquidcrystal is used (e.g. having a Grandjean or fingerprint texture). Theexact color can be tuned by the choice of materials, e.g. the choice ofliquid crystal, and for instance the polymerisation conditions,determining the effective pitch of the chiral nematic phase.

Conveniently the ratio of polymer to liquid crystal in theelectro-optically active layer may be any suitable ratio, but preferablyis in the region of 30-99.8%, more preferably 50-80%. Such polymersystems are known as polymer dispersed liquid crystal (PDLC) systems.

When the polymer system is a PDLC system, the polymer preferablycomprises a substantially continuous isotropic polymer phase, and theliquid crystalline material comprises a dispersed liquid crystallinephase.

Advantageously, the liquid crystalline phase comprises droplets ordomains, having an average diameter in the range 0.3-3 μm, preferably inthe range 1-2 μm, containing liquid crystalline material. Usually, amodal dispersion in/of the diameter of the droplets or domains isobserved.

Conveniently, the liquid crystalline phase is randomly aligned, and ofnematic nature, although in principle other liquid crystalline phases,such as chiral nematic, smectic, or discotic phases can be used too. Inthe off-state of the filament or fibre, there is a mismatch between theisotropic refractive index of the continuous polymeric phase, and thatof the randomly aligned dispersed liquid crystalline phase. Because ofthis, and the micron sized domain size of the liquid crystalline phase,light scattering will occur, resulting in a white layer.

Upon application of a voltage inducing the on-state, the director of thedispersed nematic liquid crystalline droplets will orient parallel tothe electric field, provided the liquid crystalline phase has a positivedielectric anisotropy. If the materials are chosen such that therefractive index of the polymer phase matches the ordinary refractiveindex of the liquid crystalline dispersed phase, no effective refractiveindex mismatch is experienced, and the layer will appear transparent. Aparticularly well-suited material combination is for instance, the NOA65/E7 system, that can be obtained from Norland (Cranbury, N.J., U.S.A.)and Merck (Darmstadt, Germany), respectively. The liquid crystal E7 (seeFIG. 4) is actually a eutectic mixture consisting of 50.6%4′-pentylcyanobiphenyl, 25.2% 4′-heptylcyanobiphenyl, 17.8%4′-octyloxycyanobiphenyl, and 6.4% 4′-pentylcyanoterphenyl (seeWilderbeek et al., Advanced Materials, 15(12), p. 985-988, 2003).

Examples of further materials and useful combinations are for instanceextensively described in Drzaic, P. S., “Liquid crystal dispersions”,World Scientific, Singapore, 1995. Due to the aligned director in theon-state, an off-axis refractive mismatch of the refractive indices willexist, resulting in an angle-dependent hazy appearance.

Alternatively, the polymer materials and liquid crystalline materialscan be chosen such that their respective refractive indices, i.e. theisotropic polymer refractive index and the ordinary refractive index ofthe dispersed liquid crystalline phase, match in the on-state, when anelectric field is present. In this case, the on-state is the transparentstate, and the off-state is the opaque state. Other combinations, suchas matching of the isotropic polymer refractive index with theextraordinary refractive index of the dispersed liquid crystallinephase, or using liquid crystalline materials with negative dielectricanisotropy, are also possible.

Alternatively, the electro-optically active layer comprises ananisotropic gel comprising a polymer having a polymer backbone to whichmesogenic cores are attached, and a liquid crystalline substance.

Preferably, the fibre or filament has a substantially circular crosssection, the first conductive layer comprising an inner conductive coreextending axially along the filament or fibre, and the second conductivelayer comprising an outer electrode, the electro-optically active layerbeing positioned between the inner core and the outer electrode.

Advantageously, the outer electrode is at least partially transparent.

Alternatively, the fibre or filament has a substantially square orrectangular cross section, the first conductive layer comprising abottom electrode, the second conductive layer comprising a topelectrode, and the electro-optically actively layer being positionedbetween the bottom and the top electrode layers.

According to a second aspect of the present invention there is provideda method for forming a filament or fibre comprising:

forming a first conductive layer;

applying an electro-optically active layer either directly, orindirectly, to the first conductive layer;

applying a second conductive layer, either directly, or indirectly, tothe electro-optically active layer, wherein the electro-optically activelayer is formed by:

(i) forming the electro-optically active layer from a homogeneous systemof cross linkable monomers and a non-reactive mesogen, prior to applyingthe electro-optically active layer to the first conductor;

(ii) inducing a phase change in the homogeneous system.

The phase change in the homogeneous system may take place either beforeor after application of the second conductive layer.

Preferably the step of inducing a phase change comprises illuminating orheating the filament or fibre.

According to a third aspect of the present invention there is provided amethod for forming a filament or fibre comprising:

forming a first conductive layer;

applying an electro-optically active layer either directly, orindirectly, to the first conductive layer;

applying a second conductive layer, either directly, or indirectly, tothe electro-optically active layer, wherein the electro-optically activelayer is formed by:

(i) forming the electro-optically active layer from a homogeneous systemof at least a polymer and a non-reactive mesogen, in combination with acommon solvent, prior to applying the electro-optically active layer tothe first conductor;

(ii) removing of the solvent.

The solvent may be removed before application of the second conductivelayer. This results in a heterogeneous system.

Alternatively, the solvent may be removed after application of thesecond conductive layer. This results in a homogeneous system.

Optionally, the method comprises the additional step of heating thehomogeneous or heterogeneous system.

The invention will now be further described by way of example only withreference to the accompanying drawings in which:

FIGS. 1 a and 1 b are schematic representations of a fibre according toa first embodiment of the invention.

FIG. 2 is a schematic representation of a fibre according to a secondembodiment of the present invention;

FIGS. 3 a and 3 b are schematic representations of a polymer dispersedliquid crystal optical element suitable for forming theelectro-optically active layer forming a fibre according to the presentinvention;

FIG. 4 shows the chemical composition of a non-reactive liquidcrystalline mixture E7;

FIG. 5 is a schematic representation of a set up for a continuousmanufacturing process for manufacturing a fibre or filament according tothe present invention;

FIGS. 6 a and 6 b are schematic representations of an isotropic gelsuitable for forming the electro-optically active layer forming afilament or fibre according to the present invention;

FIG. 7 shows the chemical composition of C3M and 5CB polymers suitablefor use in the present invention.

Referring to FIGS. 1 a and 1 b, fibres, according to a first embodimentof the present invention are shown schematically.

FIG. 1 a shows a fibre 2 comprising a central conductive core 4extending axially along the fibre. The core is surrounded by anelectro-optically active layer 6 which in turn is surrounded by an outerelectrode 8. The fibre 2 further comprises a protective layer 10.

It is to be understood that a conductive core according to the presentinvention is designated generally by the reference numeral 4. Althoughthe conductive core may directly consist of a conductive metal wire, theconductive core 4 may also comprise an elongate core, preferably formedfrom an electrically insulating material, the core having a core axis,and covered by an electrically conductive material. The electricallyconductive material may be fabricated in several ways, by using thinlayer deposition techniques, lithographic methods, X-ray lithography,particle beams and other non-lithographic techniques.

The electrode material can be either inorganic or organic and includes,but is not limited to, indium tin oxide, gold, silver, copper, platinum,and their derivatives, and conductive or semi-conductive oligomers orpolymers, e.g. polyaniline and thiophene derivatives such apoly(3,4-ethylenedioxythiophene): PEDT or PEDOT.

Optionally, these oligomers or polymers may contain additives tooptimise the electrical and thermal conductivity, and enhance thelifetime.

In preferred embodiments, the core is substantially cylindrical in shapeand may be formed from a non-conductive flexible polymer fibre. Examplesof suitable polymer fibres include, but are not limited to, polyesters,polyamides, polyacrylics, polypropylenes, vinyl-based polymers, wool,silk, flax, hemp, linen, jute, rayon-based fibres, celluloseacetate-based fibres and cotton.

An advantage of using polymer fibres is that they are readily availableand have mechanical properties which can be adapted to suit theparticular fibre requirement e.g. in terms of strength and flexibility.This is to be contrasted with conductive metal wires which have only alimited range of mechanical properties.

It is furthermore to be understood that the conductive core as describedabove, may optionally also include one or more additional coatings,overlaying the electrically conductive material. The primary function ofthis coating is preferably to protect the electrodes, since these are bynature very fine and delicate. However, the coating may also perform asecondary function which includes, but is not limited to, an adhesionlayer, a barrier layer, a sealing or covering layer, a UV shieldinglayer, a polarizing layer, a brightness enhancing or perceptionimprovement layer, a colouration layer, an additional conductive orsemi-conductive electrode layer, a channelling layer, a dielectric layeror any combinations thereof.

The fibre shown in FIG. 1 b has a ribbon-like or flat fibre layout. Thisfibre 12 comprises an electro-optically active layer 14 surrounded byfirst and second electrode layers 16, 18.

These basic configurations may have further layers added as appropriate,as shown in FIG. 2, and the fibre 2, 12 may not always have a protectivelayer 10.

FIG. 2 illustrates a fibre 20 comprising a central conductive core 22,an electro-optically active layer 24, an outer electrode layer 26 and aprotective layer 28. The fibre 20 comprises a first alignment layer 30positioned between the central core 22 and the electro-optically activelayer 24, and a second alignment layer 32 positioned between theelectro-optically active layer 24 and the outer electrode 26.

Again, it is to be understood that a conductive core according to thepresent invention may directly consist of a conductive metal wire, butthe conductive core 22 may also comprise a non-conductive core,preferably formed from an electrically insulating material, that iscovered by an electrically conductive material.

The fibre 20 further comprises a functional layer 34 which will bedescribed in more detail herein below.

It is to be understood that the alignment layers and the functionallayers are not essential to all embodiments of the present invention.The nature of the electro-optically active layer will determine thestructure of the fibre.

For instance, alignment layers are required in those systems where theorientation in a preferred direction is essential to the functioning ofthe electro-optical layer. For example, it may be preferred to induce awell-defined twist of the liquid crystalline director in a TN or STNdevice by aligning the liquid crystals at the boundaries of theelectro-optically active layer. As these switching principles are basedon the modulation of the polarization of the incident light, usually atleast one polarization layer is required to make the effect visible.Furthermore, additional requirements may hold for these specificsystems, such as the control over the retardation, dΔn, where d is thethickness of the electro-optically active layer and Δn is thebirefringence of the liquid crystalline phase (see for instance Gooch,C. H., Tarry, H. A., Electronics Letters, 10, p. 2, 1974, and Gooch, C.H., Tarry, H. A., J. Phys. D: Appl. Phys., 8, p. 1575, 1975.

In addition, further features may be present in the fibre, for example,thin metal wires may be wound around the outer electrode, which wiresact as an electrical shunt. Spacers may be included to define thethickness of electro-optically active layer. The spacer means arepreferably formed from a non-conductive material, such as glass orpolystyrene, and may be in the form of, for example, elongate wires orsubstantially spherical beads of specific size, or thin continuousfilaments wound around the core electrode. The wound filaments are thussituated between the core electrode and the outer electrode and definethe spacing between them.

The electro-optically active layer forming part of the fibre or filamentof the present invention, is a combination of a polymer and theelectro-optically active substance such as liquid crystalline material.

A fibre of the type shown in FIG. 2 is formed by coating an electricallyconductive fibre core using conventional methods such as dip coating,spray coating, vapour deposition, ink-jet printing, micro-contactprinting or sputtering, with a liquid crystal alignment layer such as apolyimide derivative, or a photoalignment layer.

Examples of alignment layers are extensively described in theliterature, see for instance Cognard, J., Mol. Cryst. Liq. Cryst. Suppl.Ser., 1, p. 1-77, 1982. Non-limitative examples are polyimide layers,photoorientable layers, such as coumarin-based or cinnamate-basedpolymers or layers consisting of surfactants. Also, mechanicalinteraction with the fibre core may induce the preferred alignment ofthe liquid crystals.

The use of a polyimide alignment layer can be advantageous as therubbing conventionally required for inducing the desired alignment canbe directly accomplished via the manufacturing method. However,mechanical rubbing introduces defects and is a source of electrostaticdischarge and dust.

Preferably, photoalignment layers are used, as the alignment can beinduced by illumination which is a non-contact method (see for instanceSchadt, M. et al., Nature, 381, p. 212, 1996, and Wilderbeek et al.,Advanced Materials, 15(12), p. 985, 2003).

The liquid crystal alignment layer is conventionally finalized usingheat curing or UV-irradiation and effects a pre-tilt angle of 3 to 4°.This pre-tilt is required to lower the threshold voltage for switching,and to control the rotation direction of the liquid crystals, thusreducing for instance the formation of disclinations.

The fibre is subsequently coated by applying an electro-optically activelayer either directly, or indirectly, to the first conductive layer.

The electro-optically active layer can be formed using severalprocedures:

(i) directly, by applying an inhomogeneous polymer/LC system directly tothe fibre. Usually, the rheology of such a system is paste-like,allowing for the practical deposition on the fibre.

(ii) indirectly, by applying a homogeneous polymer/LC system directly tothe fibre, using a suitable common solvent to the polymer and mesogen.Upon removal of the solvent, e.g. by evaporation or curing, the finalmorphology is established as a coating on the fibre.

(iii) Indirectly, by in-situ generation, using an initially homogeneousmixture of crosslinkable monomers and a non-reactive mesogen. Afterapplication of the mixture on the fibre, phase separation is inducedeither

a. Thermally

b. By (photo-)chemical means.

Optionally, a second alignment layer may be applied to theelectro-optically active layer. A second electrode is then applied tothe second alignment layer, or directly to the electro-optically activelayer.

The second electrode may be applied to the electro-optically activelayer before, or after the layer has been formed.

Usually, the fibre, or stack is covered by a protective cover layer toprotect the electro-optic substance 6 and to provide additionalstability and support in the fibre 2 or 12. Preferably the protectivecover is formed from a non-conductive material and is at least partiallytransparent to light. Conveniently, the protective cover is formed froma flexible polymer.

Various polymers/liquid crystal composites may be used. One suchcomposite is a polymer dispersed liquid crystal system (PDLC) containinga relatively high, for example, 50 to 80% polymer content. Such a systemcomprises a continuous isotropic polymer phase and a dispersed lowmolecular weight micron sized liquid crystalline phase.

Referring to FIGS. 3 a and 3 b, such a system is shown initially in theoff-state in FIG. 3 a and then in the on-state in FIG. 3 b. The systemcomprises an isotropic polymer phase 36 and a dispersed low molecularweight micron sized liquid crystalline phase 38.

In the off-state shown in FIG. 3 a, there is a mismatch between theisotropic refractive index of the continuous polymeric phase, and thatof the randomly aligned dispersed liquid crystal phase. Because of this,and the micron sized domain size, light scattering will occur, resultinga white layer.

Preferably, the liquid crystalline phase is a nematic phase, although inprinciple other liquid crystalline phases, such as chiral nematic,smectic, or discotic phases can be used too.

Upon application of a voltage in the on-state as shown in FIG. 3 b, thedirector of the dispersed nematic liquid crystalline droplets 38 willorient parallel to the electric field, provided the nematic liquidcrystal has a positive dielectric anisotropy.

If the materials are chosen such that the refractive index of thepolymer 36 matches the ordinary refractive index of the dispersed liquidcrystalline phase 38, no effective refractive index mismatch isexperienced and the layer will appear transparent.

A particular well-suited material combination illustrated in FIG. 4 isfor instance the NOA 65/E7 system, that can be obtained from Norland(Cranbury, N.J., U.S.A.) and Merck (Darmstadt, Germany), respectively.The liquid crystal E7 is actually a eutectic mixture consisting of 50.6%4′-pentylcyanobiphenyl, 25.2% 4′-heptylcyanobiphenyl, 17.8%4′-octyloxycyanobiphenyl, and 6.4% 4′-pentylcyanoterphenyl (seeWilderbeek et al., Advanced Materials, 15(12), p. 985-988, 2003).Another example consists of the epoxy EPON 828 (Shell Chemical Co.), thecuring agent Capcure 3800 (Miller-Stephenson Chemical Co.), and theliquid crystal E7. Yet another example consists ofpolymethylmethacrylate (PMMA) and the liquid crystal E7, using thecommon solvent chloroform. Examples of further materials and usefulcombinations are for instance extensively described in Drzaic, P. S.,“Liquid crystal dispersions”, World Scientific, Singapore, 1995. Due tothe aligned director in the on-state, shown in FIG. 3 b, an off axisrefractive mismatch of the refractive indices will exist, resulting inan angle dependent hazy appearance. This type of polymer/liquid crystalcomposite system may be generated in situ, as described above, byinducing a phase separation from an initially homogeneous system ofcrosslinkable monomers and a non-reactive mesogen. The phase separationis either induced thermally, by evaporation of a co-solvent, or bychemical or photochemical means.

During the course of these processes, phase separation into polymer-richand polymer-poor regions will occur, and the final morphology can beaccurately tuned, depending on the proper process conditions.

An advantage of such a system is the resulting mechanical stability. Theoverall characteristics of the electro-optically active layer are thatof a solid-like material.

In addition, polarizers and alignment layers are not required as theswitching principle of a PDLC is based on scattering, rather thanmodulation of the polarization of the incident light. Thus, the exactalignment of the liquid crystals at the boundaries of theelectro-optically active layer is not required. In fact, in theoff-state, the mesogenic molecules adopt a random director profile thatvaries from one droplet or domain to the other droplet or domain.

Furthermore, the concept is suited for production in a continuousprocess. The phase separation kinetics can be very fast, and phaseseparation can be achieved within minutes to several seconds, allowingfor reel-to-reel fabrication.

FIG. 5 shows a schematic set-up for a continuous manufacturing processfor a fibre or filament according to the present invention. A fibre 52is drawn through a fluid containing reservoir 54 from reel 62 to reel64, via rollers 66, 68. The fibre is subsequently coated with themixture. Formation of the desired morphology can be realized via themethods described herein. Optionally, the morphology may be establishedusing the illumination sources 58 situated after the fluid reservoir.

Optionally, additional reservoirs (not shown) may be present before orafter the reservoir 54, for instance to apply different coatings, suchas a second electrode, cover layer, alignment layers, adhesion promotionlayers, wetting layers, polarizers, brightness enhancement layers,before the fibre is wound up again.

A screen may 56 be used to shield the material present in the fluidreservoir 54 from the light coming from the one or more illuminationsources 58 present, such as UV light sources, in order to preventpremature induced chemical or physical changes, such as phase separationand/or polymerisation and/or precipitation and/or degradation, of thematerial present in the reservoir. A small opening 60 in the screenenables the transport of the fibre from reel 62 to reel 64. Although thescreen 56 shown in FIG. 5 has a flat and rectangular layout, the actualshape may differ as long as its shape fulfils the role of shielding thecontents of the reservoir 54 from the light coming from the lightingsources 58. For example, a small diaphragm may be used directly at theedge of the fluid reservoir.

The illumination sources 58 can be of various types, but preferably emitor radiate light with a wavelength in the visible to UV region. UV-lightsources are particularly appropriate, and for instance medium or highpressure mercury light sources may be used. Optionally, the heat that isproduced by these type of lamps can be blocked by placing an infraredscreen (not shown), that is transparent to the wavelength required toinduce the desired phase change of the electro-optical layer, in betweenthe light source and the fibre 52.

The fibre 52 is transported from its origin, preferably from reel 62 toits destination, or reel 64 with a velocity v (m s-1). The velocity ofthe fibre is determined by the angular velocity w (rpm or rad s-1) ofthe reels, as imposed by for instance an electrical motor (not shown).

Preferably, the entire set-up or parts of the set-up can be placed in anenclosure (not shown) that enables control over the environment withrespect to the gas conditions. For instance, it may be advantageous toprocess and/or illuminate the fibre and/or electro-optical layer in aninert atmosphere, such as nitrogen, helium or argon or mixtures thereof,or to process and/or illuminate the fibre and/or electro-optical layerin a pressurized environment different from atmospheric condition (e.g.vacuum, reduced pressure, high pressure).

Good voltage transmission characteristics can be obtained ranging fromapproximately 1V per micron to 0.5V per micron, across theelectro-optically active layer.

The electro-optically active layer described above is suited to producereflective fibres, as the degree of front and back scattering can beaccurately tuned by the processing methods as described herein, and asfor instance described by Cornelissen, H. J. et al., Proceedings of the17th International Display Research Conference, Toronto (Canada), p.144, 1997.

Optionally, dyes can be added to the polymer/liquid crystal composite inorder to produce colour changes in the fibre.

EXAMPLE 1

A flexible polyester foil (polyethyleneterephtalate) coated with a thinconductive layer of poly(3,4-ethylenedioxythiophene) was covered with areactive mixture consisting of 60% w/w of multifunctional reactivemonomers (NOA65, Norland, Cranbury, N.J., U.S.A.) and 40% w/w of aeutectic liquid crystalline mixture (E7, Merck, a mixture consisting ofcyanobiphenyls and one cyanoterphenyl, as specified herein). The layerthickness was tuned accurately by using spacers with well-definedthickness by spincoating. Upon irradiation with UV-light, the polymerdispersed liquid crystal is formed. A second electrode, e.g., a secondpolyester foil with conductive coating, can be applied before or afterirradiation. The resulting flexible foil or ribbon-like fibre can beswitched between a scattering state and a transparent state with amoderate voltage (10-40V).

EXAMPLE 2

A conductive core fibre (copper, fibre diameter 120 μm) was coated bypassing the fibre horizontally through a reservoir containing a mixtureof 60% w/w reactive multifunctional monomers (NOA65, Norland, Cranbury,N.J., U.S.A.) and 40% w/w of a eutectic liquid crystalline mixture (E7Merck, a mixture consisting of cyanobiphenyls and one cyanoterphenyl, asspecified herein). The reservoir was 4.0 mm in diameter and 10.0 mm inlength. The relative intended thickness of the coating or the ratio ofthe coating and the conductive fibre radius (e/b) was controlled by thefollowing parameters:

-   -   The speed v at which the conductive fibre travels through the        reservoir (which is in turn adjusted by the power supplied to        the motor)    -   The capillary number Ca: ${Ca} = \frac{\eta \cdot v}{\gamma}$

(where η is the viscosity, and γ is the surface tension of the uncuredmaterial).

For an uncured coating of 10 μm thickness with a viscosity of 0.5 Pa·sand a surface tension of 0.037 N/m, the speed was 3.0 mm/s. Curingoccurred with medium pressure mercury lamps, situated directly after thefluid reservoir.

A polymer/liquid crystalline material composite may also be formed usinganisotropic monomers rather than isotropic monomers.

Such systems may be produced by photopolymerisation of small amounts ofanisotropic monomers in the presence of a non-reactive low molecularweight liquid crystalline solvent. Typically, acrylates, methacrylates,or epoxides are used for the anisotropic monomers, and a well-describedexample consists of the reactive mesogenic acrylate monomer benzoicacid, 4-[3-[(oxo-2-propenyl)oxy]propoxy]-,2-methyl-1,4-phenylene ester(C3M) and the non-reactive liquid crystal 5CB (4′-pentyl,[1,1-biphenyl]-4-carbonitrile), as shown in FIG. 7. See for instanceHikmet, R. A. M. in “Liquid crystals in complex geometries. Formed bypolymer and porous networks”, Crawford, G. P., Zumer, S. (Eds.), Chapter3, Taylor & Francis, London, 1996, and Wilderbeek et al., Jpn. J. Appl.Phys., Part 1, 41 (4A), p. 2128, 2002.

Photopolymerisation of initially homogeneous mixtures of an anisotropicmonomers and low molecular weight liquid crystalline solvents producesphase separation of the liquid crystalline polymeric structure intopolymer-rich and polymer-poor phases. Depending on the molecularstructure of the monomer used, the formed polymers are either side-chainor chemically crosslinked structures, both consisting of a polymerbackbone to which mesogenic cores are attached. Such polymers are knownas anisotropic gels or plasticized liquid crystalline networks and areschematically illustrated in FIGS. 6 a and 6 b described herein below.

The alignment direction of the mesogens in the network reflects theinitial alignment of the mixture. In this way, a planarly (horizontally,in the plane of the fibre) or homeotropically (vertically, perpendicularto the plane of the fibre) oriented network can be created. The initialalignment is dictated by interfacial interactions between the LC mixtureand alignment layers such as the before described examples of rubbedpolyimide or photoalignment layers.

FIGS. 6 a and 6 b show schematically an anisotropic gel initially in theoff-state in FIG. 6 a, and then in the on-state in FIG. 6 b. Theanisotropic gel comprises polymer chains 40 with mesogenic side-chains42, and non-reactive mesogens 44.

In the off-state, when no electrical field is applied, the inert liquidcrystal solvent molecules are aligned with the mesogenic units of thenetwork. Consequently, due to the refractive index match between themesogenic units of the network and those of the inert liquid crystalsolvent molecules, incident light is not scattered, and the system willappear transparent.

However, in the presence of an electrical field, the liquid crystalsolvent molecules will reorientate along the field lines. Lightscattering will occur due to the induced domain formation, and theresulting refractive index mismatch, and the system will become opaque.

Fibres incorporating such electro-optically active layers do not requirepolarizers, as the switching principle is based on the inducedscattering resulting from the refractive index mismatch in the on-state,rather than modulation of the polarization state of the incident light,and can produce fast switching fibres, as the mesogenic units in thepolymer network provide the internal director field that forms thedriving force for relaxation to the aligned state in the field-offcondition. The fibres have good mechanical stability, and there isalmost no viewing angle dependency due to the refractive index matchingbetween the low molecular weight LC component and the mesogenic moietiesof the network.

Alignment layers are, however, required when using such anelectro-optically active substance, since the alignment direction of themesogens in the network reflects the initial alignment of the mixture,which in turn is dictated by the interfacial interactions between the LCmixture and alignment layers.

The term “polymer” as used hereinabove, should be understood to includealso the term “oligomer”.

1. A filament or fibre (2) comprising: a first conductive layer (4); anelectro-optically active layer (6); a second conductive layer (8);wherein the filament or fibre has an off-state and an on-state, theelectro-optically active layer comprising a combination of anelectro-optically active substance and a polymer.
 2. A filament or fibreaccording to claim 1 wherein the electro-optically active substancecomprises a liquid crystalline material.
 3. A filament or fibreaccording to claim 1 wherein the polymer content is substantiallybetween 0.5 to 40%.
 4. A fibre or filament according to claim 1 whereinthe electro-optically active substance comprises ferro-electric phase.5. A filament or fibre according to claim 1 wherein the polymer contentis substantially between 30% to 99.8%.
 6. A filament or fibre accordingto claim 1 wherein the polymer comprises a substantially isotropicpolymer phase, and the liquid crystalline material comprises a dispersedliquid crystalline phase.
 7. A filament or fibre according to claim 5wherein the liquid crystalline phase comprises liquid crystallinedomains having an average diameter of approximately 0.5-2 μm.
 8. Afilament or fibre according to claim 5 wherein the electro-opticallyactive layer comprises a polymer comprising a polymer backbone (40) towhich mesogenic cores (42) are attached, and a liquid crystallinesolvent.
 9. A filament or fibre according to any one of claim 5 wherethe liquid crystalline material comprises a liquid crystalline director,which director is controlled uniaxially.
 10. A filament or fibreaccording claim 5 wherein the liquid crystalline material comprises aliquid crystalline director, which director is controlled biaxially. 11.A filament or fibre according to claim 9 further comprising an alignmentlayer for enforcing the director control.
 12. A filament or fibreaccording to claim 9 wherein, in one of the on-state or the off-state,the refractive index of the polymer is different to that of the liquidcrystalline material, for a predetermined wavelength of incident light.13. A filament or fibre according to claim 12, wherein in the other ofthe on-state or the off-state, the refractive index of the polymermatches the ordinary refractive index of the liquid crystallinematerial.
 14. A filament or fibre according to claim 12 wherein theelectro-optically active layer comprises an anisotropic polymer.
 15. Afilament or fibre according to claim 12 wherein the electro-opticallyactive substance comprises material possessing a smectic phase.
 16. Afilament or fibre according to claim 12 wherein the electro-opticallyactive substance comprises material possessing a chiral nematic phase orcholesteric phase, optionally induced by a chiral dopant.
 17. A filamentor fibre according to claim 12 wherein the polymer is at least partlybased on non-covalent, supramolecular interactions.
 18. A fibre orfilament (2) according to claim 12 having a substantially circularcross-section, the first conductive layer (4) comprising an innerconductive core extending axially along the filament or fibre, and thesecond conductive layer (8) comprising an outer electrode, theelectro-optically active layer (6) being positioned between the innercore and the outer electrode.
 19. A fibre or filament according to claim18 wherein the outer electrode is at least partially transparent.
 20. Afibre or filament according to claim 18 further comprising a firstcoating layer completely or partially coating the conductive core.
 21. Afibre or filament according to any one of claim 18 further comprising asecond coating layer positioned between the electro-optically activelayer and the outer electrode.
 22. A fibre or a filament according toany one of claim 18 where the or each coating layer comprises analignment layer.
 23. A fibre or filament according to any one of claim18 further comprising one or more metal wires wound around the outerelectrode.
 24. A fibre or filament according to any one of claim 18further comprising spacers positioned between the inner electrode andthe outer electrode.
 25. A fibre or filament according to claim 24wherein the spacers are formed from a non-conductive material.
 26. Afibre or filament according to claim 15 having a substantially square orrectangular cross-section, the first conductive layer (18) comprising abottom electrode, the second conductive layer (16) comprising a topelectrode, and the electro-optically active layer (14) being positionedbetween the bottom and top electrode layers.
 27. A method for forming afilament or fibre (2) comprising: forming a first conductive layer (4);applying an electro-optically active layer (6) either directly, orindirectly, to the first conductive layer; applying a second conductivelayer (8), either directly, or indirectly, to the electro-opticallyactive layer, wherein the electro-optically active layer is formed by:(i) forming the electro-optically active layer from a homogeneous systemof cross linkable monomers and a non-reactive mesogen, prior to applyingthe electro-optically active layer to the first conductor; (ii) inducinga phase change in the homogeneous system.
 28. A method according toclaim 27 wherein the phase change is induced before application of thesecond conductive layer.
 29. A method according to claim 27 wherein thestep of inducing a phase change comprises heating the filament or fibre.30. A method for forming a filament or fibre comprising: forming a firstconductive layer; applying an electro-optically active layer eitherdirectly, or indirectly, to the first conductive layer; applying asecond conductive layer, either directly, or indirectly, to theelectro-optically active layer, wherein the electro-optically activelayer is formed by: (i) forming the electro-optically active layer froma homogeneous system of at least a polymer and a non-reactive mesogen,in combination with a common solvent, prior to applying theelectro-optically active layer to the first conductor; (ii) removing ofthe solvent.
 31. A method according to claim 30 wherein the solvent isremoved before application of the second conductive layer.